Polyester production process and reactor apparatus

ABSTRACT

The invention provides a polyester production process by bulk polymerization in a reactor, wherein the volume of the resulting polyester is shrunk for a release from the inner surface of the reactor, so that the polyester can be recovered in the form of a bulky mass. The invention also provides a reactor for bulk polymerization for polyester, which comprises an inner surface that enabling the resulting polyester to be released therefrom upon its volume shrinkage.

TECHNICAL FIELD

[0001] The present invention relates generally to a polyester productionprocess, and more particularly to a process for the production ofpolyesters by bulk polymerization in a reactor, which enables thepolyester product to be easily recovered in a bulky mass form after thecompletion of polymerization reaction. The present invention is alsodirected to a reactor apparatus for the bulk polymerization forpolyesters, which is suited for use with such a polyester productionprocess.

[0002] The inventive production process and apparatus disclosed hereinlend themselves to the production of crystalline, biodegradablealiphatic polyesters such as polyglycolic acid.

BACKGROUND ART

[0003] Polyesters such as polyglycolic acid have often been produced bybulk polymerization. In batch manners, however, it has sometimes beendifficult to take and recover polyester products out of a reactorapparatus after the completion of polymerization reactions. This is nowexplained more specifically with reference to polyglycolic acid as anexample.

[0004] As can be seen from the following formula (1):

[0005] polyglycolic acid may be synthesized through thede-hydration-polycondensation of glycolic acid.

[0006] Polyglycolic acid may also be synthesized through thedealcoholization-polycondensation of an alkyl ester of polyglycolicacid, as can be noted from the following reaction scheme (II):

[0007] Here R is an alkyl group that has preferably about 1 to 5 carbonatoms.

[0008] Moreover, polyglycolic acid may be synthesized by thering-opening polymerization of glycolide that is a bimolecular cyclicester of glycolic acid or, alternately, called a “cyclic dimer”according to the following scheme (III):

[0009] The glycolic acid synthesized by the ring-opening polymerizationof glycolide is sometimes referred to as poly-glycolide.

[0010] The polyglycolic acid (or polyglycolide) formed through thesepolymerization reactions is usually synthesized by bulk polymerizationbecause of being only soluble in a specific solvent such ashexafluoroiso-propanol. The bulk polymerization is usually carried outby two production processes, i.e., a continuous process and a batchprocess.

[0011] Japanese Patent Laid-Open No. (JP-A) 03-502115 discloses aprocess wherein bulk polymerization for cyclic esters is carried out ina twine-screw extruder.

[0012] JP-A 07-26001 discloses a process for the polymerization forbiodegradable polyester-based polymers, wherein a bimolecular cyclicester of hydroxycarboxylic acid and one or more lactones arecontinuously fed to a continuous reaction apparatus having a staticmixer for ring-opening polymerization.

[0013] JP-A 07-53684 discloses a process for the continuouspolymerization for aliphatic polyesters, wherein a cyclic dimer ofhydroxycarboxylic acid is fed together with a catalyst to an initialpolymerization step, and then continuously fed to a subsequentpolymerization step built up of a multiple screw kneader.

[0014] These continuous production processes are well suitable for themass production of polyesters such as polylactic acid or polyglycolicacid, but they are not suitable for cases where the volume of productionis low and there are a wide variety of products to be produced. There isalso demand for polyesters such as polyglycolic acids having variousmolecular weights and copolymers of glycolic acid with other comonomers,which are to be produced in the small amount and large variety.

[0015] Generally, batch processes rather than continuous ones lendthemselves to flexible production of polyesters. When bulkpolymerization is carried out in a reactor in a batch productionfashion, however, it is difficult to remove the resulting polyglycolicacid out of the reactor, because its viscosity is high enough to showstickiness in its molten state.

[0016] For instance, U.S. Pat. No. 2,668,162 shows in Example 3 thatglycolide is heated in a tubular reaction vessel, thereby obtaining apolymer. In this case, however, scraping. extrusion, pumping or othermeans should be used to discharge the resulting polymer from the tubularreaction vessel in a troublesome, time-consuming manner. In addition,there is another need for removal of the remaining polymer depositedonto the inner wall of the reaction vessel. Example 4 refers to anexperimental example wherein the reaction of glycolide and lactide iseffected with the application of heat in the reaction vessel; however,this example reveals that after 1 hour, the stirring operation isstopped because the reaction product is too viscous. It is not easy toremove such a viscous reaction product from the stirrer. To dischargethe resulting polymer from the reactor, it should be first solidified bycooling and then pulverized.

[0017] U.S. Pat. No. 3,297,033 describes that a mixture of glycolidewith a polymerization catalyst is heated in a separate glass tube forpolymerization and the product is then cooled to obtain a polymer (seeExample 1). However, the resulting polyglycolic acid has a high meltingviscosity and stickiness to the glass surface, and so cannot easily beremoved out of the glass tube even upon cooling. When the resultingpolyglycolic acid is removed by cooling it and breaking the glass tube,glass pieces stick to a bulky form of polyglycolic acid. In this case,some operation is needed for removal of glass pieces from polyglycolicacid. This operation itself is troublesome, and the yield of polymerrecovery drops as well.

[0018] According to one possible approach, the resulting polyester isheated for its removal from the reactor in a molten state. However, whenthe polyester is too viscous, it is required to elevate the heatingtemperature. This renders undesired reactions such as decomposition anddiscoloration of the polyester likely to occur. The polyester in amolten state is hard to handle. Even with this approach, it is stilldifficult to prevent deposition of some polyester to the wall of thereactor, the stirrer, etc.

DISCLOSURE OF THE INVENTION

[0019] One object of the present invention is to provide a polyesterproduction process by bulk polymerization in a reactor apparatus, whichenables the resulting polyester to be readily recovered in a bulky formafter the completion of polymerization reactions.

[0020] Another object of the present invention is to provide a polyesterbulk polymerization reactor apparatus best suited for such a polyesterproduction process.

[0021] As a result of intensive studies made to accomplish the aforesaidobjects, the inventors have figured out a process wherein a reactorapparatus having an inner surface enabling the resulting polymer to bereleased upon its volume shrinkage is used to produce a polyester bybulk polymerization, and the volume of the resulting polyester is shrunkto release the polyester from the inner surface of the reactor, so thatthe polyester can be recovered as a bulky mass from the reactor.

[0022] According to the production process of the present invention, itis possible to make use of the releasability of the resulting polyesterfrom the inner surface of the reactor so that the polyester can beproduced by simple means yet at high recovery yield. Accordingly, theproduction process and system of the present invention are suitable forcases where the polyester is produced in the small amount and largevariety by bulk polymerization. These findings have underlain thepresent invention.

[0023] Thus, the present invention provides a process for the productionof a polyester by bulk polymerization in a reactor apparatus,characterized in that the volume of the resulting polyester is shrunk torelease the polyester from the inner surface of the reactor, so that thepolyester can be recovered in a bulky form from the reactor.

[0024] The present invention also provides a polyester bulkpolymerization reactor apparatus capable of being heated from outsideand formed of a material having heat resistance enough to stand up tothe bulk polymerization temperature for polyesters, and comprises aninner surface that enables the resulting polyester to be released uponits volume shrinkage.

BEST MODE FOR CARRYING OUT THE INVENTION

[0025] 1. Polyesters

[0026] The polyesters used herein, for instance, include polycondensatesof dicarboxylic acids and diols, poly-condensates of hydroxycarboxylicacids, polycondensates of alkyl esters of hydroxycarboxylic acids, andring-opening polymers of cyclic esters. These may be in the form ofeither homopolymers or copolymers (copolyesters).

[0027] Aliphatic polyesters are preferred for the polyesters in view ofbiodegradability, and prefered aliphatic polyesters include apolyhydroxycarboxylic acid. The polyhydroxycarboxylic acid may besynthesized in the form of a polycondensate of a hydroxycarboxylic acidor an alkyl ester of hydroxycarboxylic acid. The poly-hydroxycarboxylicacid may also be synthesized in the form of a ring-opening polymer of acyclic diester (cyclic dimer) of hydroxycarboxylic acids.

[0028] The hydroxycarboxylic acids used herein, for instance, includeglycolic acid, L-lactic acid, D-lactic acid, α-hydroxybutyric acid,α-hydroxyisobutyric acid, α-hydroxyvaleric acid, α-hydroxycaproic acid,α-hydroxy-isocaproic acid, α-hydroxyheptanoic acid, α-hydroxy-octanoicacid, α-hydroxydecanoic acid, α-hydroxymyristic acid andα-hydroxystearic acid, which may have been substituted by alkyls.

[0029] The alkyl esters of hydroxycarboxylic acids are the esters ofthese hydroxycarboxylic acids and alcohols. Although salts (e.g., Nasalts) of hydroxycarboxylic acids may be used, it is noted that duringbulk polymerization, byproducts are likely to occur by way of desaltingreactions. Of these, glycolic acid and lactic acids as well as theiralkyl esters are preferred although glycolic acid and its alkyl estersare more preferred.

[0030] Of the cyclic esters, preference is given to glycolide that isthe cyclic diesters of glycolic acids and L-lactide and D-lactide thatare the cyclic diesters of lactic acids, although glycolide isparticularly preferred. The ring-opening polymerization of glycolidegives polyglycolic acid, and the ring-opening polymerization of lactidesgives polylactic acids. Glycolide may be copolymerized with lactides.

[0031] Although no particular limitation is imposed on how to produceglycolide, it is understood that glycolide may generally be obtained bythe thermal depolymerization of glycolic acid oligomers. For thedepolymerization processes for glycolic acid oligomers, for instance,use may be made of a molten depolymerization process such as one setforth in U.S. Pat. No. 2,668,162, a solid-phase depolymerization processsuch as one set forth in JP-A 2000-119269, and a solutiondepolymerization process such as one set forth in JP-A 09-328481. Usemay also be made of glycolide obtained in the form of a cycliccondensate of chloroacetic acid salt, as reported by K. Chujo et al. inDie Makromoleculare Cheme, 100(1967), pp. 262-266.

[0032] Glycolide and lactide may be independently a ring-opening polymeror they may be a ring-opening copolymer. Glycolide and lactide may becopolymerized with other comonomers. The comonomers used herein, forinstance, include ethylene oxalate (i.e., 1,4-dioxane-2,3-dione),lactones (e.g., β-propiolactone, β-butyrolactone, pivalolactone,γ-butyrolactone, δ-valerolactone, β-methyl-δ-valerolactone, andε-caprolactone), cyclie monomers such as trimethylene carbonate and1,3-dioxane; hydroxy-carboxylic acids such as lactic acid,3-hydroxypropanoic acid, 3-hydroxybutanoic acid, 4-hydroxybutanoic acidand 6-hydroxycaproic acid or their alkyl esters; and substantiallyequimolar mixtures of aliphatic diols such as ethylene glycol and1,4-butanediol and aliphatic dicarboxylic acids such as succinic acidand adipic acid or their alkyl esters. These may be used in combinationof two or more.

[0033] Of these comonomers, preference is given to lactones, cycliccompounds such as trimethylene carbonate, and hydroxycarboxylic acidssuch as lactic acid and glycolic acid, because they are easilycopolymerizable and enable copolymers having improved physicalproperties to be easily obtained.

[0034] The comonomer(s) should be used in an amount of not more than 50%by weight, preferably not more than 45% by weight, more preferably notmore than 30% by weight, and even more preferably not more than 10% byweight of all the charged monomers. By copolymerization, for instance,it is possible to lower the melting point and, hence, processingtemperature of polyglycolic acid, and control the crystallizationtemperature thereof, thereby improving the processability thereof onextrusion or stretching.

[0035] Of a variety of polyesters, particular preference is given topolyglycolic acid because a crystalline polymer having a high molecularweight (high melting viscosity) can be readily obtained by bulkpolymerization. This polyglycolic acid should preferably be synthesizedby the polycondensation of glycolic acid or an alkyl ester of glycolicacid or the ring-opening polymerization of glycolide.

[0036] As already mentioned, the polyglycolic acid may be a homopolymer;however, it may be a copolymer (copolyester) with other comonomer(s)provided that its crystallinity be not largely affected. The copolymershould contain poly-glycolic acid in an amount of at least 50% byweight, preferably at least 55% by weight, and more preferably at least70% by weight. As the content of polyglycolic acid repeating units inthe copolymer becomes too low, the crystallization properties of thecopolymer becomes low, and so long time is needed for crystallizationwith decreased crystallinity, resulting in a drop of the ability of thecopolymer to be released or discharged from the reactor.

[0037] 2. Bulk Polymerization

[0038] The bulk polymerization according to the present invention may becarried out under the conditions preferable for polyester synthesis. Byway of example but not by way of limitation, the polymerizationcatalysts for polyhydroxycarboxylic acids such as polyglycolic acidinclude tin base compounds such as tin halides (e.g., tin dichloride andtin tetrachloride) and organic carboxylic acid tin compounds (e.g., tinoctanoate): titanium base compounds such as alkoxytitanate; zirconiumbase compounds such as zirconium acetylacetone, and antimony halides.The amount of the catalyst used is, for example, in the range ofpreferably 1 to 1,000 ppm, and more preferably 3 to 300 ppm on a weightratio basis relative to the cyclic ester.

[0039] For weight-average molecular weight control, higher alcohols suchas lauryl alcohol may be added as a molecular weight control agent. Forthe purpose of improvements in physical properties, polyhydric alcoholssuch as glycerin may also be added.

[0040] The polymerization temperature may be determined in the rangefrom 120° C. that is a substantial polymerization start temperature to250° C. More exactly, the polymerization temperature should be in therange of preferably 130 to 240° C., more preferably 140 to 230° C., andeven more preferably 150 to 225° C. Too high polymerization temperatureswould make the resulting polymer susceptible to thermal decomposition.Although the polymerization temperature may be kept constant duringpolymerization reactions, it is acceptable to elevate or lower thepolymerization temperature in a stepwise manner or a continuous manner,if required.

[0041] The polymerization time should be in the range of 3 minutes to 50hours, and preferably 5 minutes to 30 hours. Too short a polymerizationtime makes the sufficient progress of polymerization difficult. In somecases, it is difficult to release and discharge the resulting polymerfrom the inner surface of the reactor even upon solidification bycooling. Too long a polymerization time makes the resulting polymervulnerable to thermal decomposition.

[0042] Usually, the bulk polymerization may be carried out by heating amixture of a monomer(s) such as glycolic acid or glycolide, apolymerization catalyst(s) and a molecular weight control agent that isadded if required. When poly-condensation is carried out by dehydrationor de-alcoholization as is the case with polyglycolic acid or its alkylester, the reaction system should be placed under reduced pressureconditions for removal of water or alcohols therefrom.

[0043] 3. Reactor Apparatus

[0044] The reaction apparatus used herein is a reactor apparatus capableof being heated from outside and formed of a material having heatresistance enough to stand up to the bulk polymerization temperature forpolyesters and including an inner surface that enables the resultingpolyester to be released upon its volume shrinkage.

[0045] A crystalline polyester such as polyglycolic acid is formed in amolten state upon bulk polymerization; however, this polyester is shrunkin volume upon crystallization. The volume of the resulting polyester isalso shrunk by cooling. Making use of this volume shrinkage, thepolyester is released from the inner surface of the reactor so that itcan be readily discharged from the reactor.

[0046] Preferably, the reactor should not have asperities that may comeinto contact with the polyester when it is discharged out of the reactorand so disturb the smooth discharge of the polyester. It is alsopreferable that there is no stirrer within the reactor. When the moltenpolyester is deposited onto the asperities or stirrer, some scraping orgrounding operation is needed for the recovery of the polyester. Thisoperation is troublesome and time-consuming, and causes the yield ofrecovery to drop as well.

[0047] The inner surface (wall) of the reactor that is to come intocontact with the polyester should be formed of a material that enables apolyester such as polyglycolic acid to be readily released therefrom.When the inner surface of the reactor that comes into direct contactwith the polyester such as crystallized polyglycolic acid is formed of ametallic material, it has been found that the releasability of thepolyester therefrom is improved. When versatile polyesters are producedin small amounts, glass reactors such as glass test tubes are generallyused. However, if the inner surface of a reactor is made of a glassmaterial, it is likely to stick to the resulting polyester such aspolyglycolic acid.

[0048] The materials used to form at least the inner surface of thereactor, for instance, include carbon steel, stainless steel (SUS),titanium, Hastelloy, aluminum, copper, silver, gold, platinum, chromium,nickel and zinc or their alloys. These metal materials may be formed byplating on the inner surface of the reactor. All things consideredinclusive of the processability, cost effectiveness, robustness andcorrosion resistance of the reactor, stainless steel (SUS) is believedto be the most effective material.

[0049] The surface roughness of the inner part of the reactor is notcritical; however, it is preferable to buff the inner surface of thereactor (e.g., with buff No. 300), thereby improving the ability of theresulting polyester to be released and discharged from the reactor.

[0050] To improve or enhance the ability of the resulting polyester tobe released or discharged from the inner surface of the reactor, it isacceptable to apply a releasing agent thereon or coating apolytetrafluoro-ethylene or other fluoroplastic material layer thereon.

[0051] Preferably but not exclusively, the reactor should be configuredwith a wide opening. For small-batch production, it is preferable to usea metal or other tube open at both ends, or a metal or other tube closedat one end to define a bottom and open at the other end. When a tubularreactor open at both ends is used, at least one opening is closed upwith a rubber stopper, etc. Such a tubular reactor is simple instructure and easy to build up and maintain. The tubular reactor usedherein may have any desired sectional shapes inclusive of circular, ovalor polygonal shape although a tubular reactor of circular shape insection is most preferred.

[0052] When the tubular reactor used is of circular shape in section,its size should be preferably 55 mm or smaller for the purpose ofreducing variations of the melt viscosity of the resulting polyester,and preferably 30 mm or smaller in view of prevention of discolorationof the resulting polyester. This size is that of the shortest side whenthe tubular reactor is of oval, polygonal or other shape. To ensure easyremoval of a bulky form of polyester product, the size of sectionalshape should be preferably 10 mm or greater, and more preferably 20 mmor greater.

[0053] The tubular reactor should preferably have a tapered structurebecause the discharge of the resulting polyester can be more easilyachieved. The tapered structure should then preferably have a gradientin the range of 1 to 50%. With a gradient of less than 1%, any tapereffect is not obtained, and with a gradient of greater than 50%, thedischarge or handling of the resulting polyester often becomesdifficult. The resulting polyester is discharged through a wide openingin the tubular reactor having a tapered structure. When the tubularreactor has a tapered structure, the aforesaid size of sectional shapeis understood to refer to the size of an intermediate part of saidtubular reactor.

[0054] 4. Production Process

[0055] The monomers for polyester such as glycolic acid and glycolideare charged in the reactor. Usually and as desired, additives such aspolymerization catalysts and molecular weight control agents are mixedwith these monomers to prepare a mixture, which is then charged in thereactor. When the reactor used is in tubular form open at both ends, oneopening is previously closed up with a rubber stopper, etc.

[0056] No particular limitation is imposed on how to charge the monomer,polymerization catalyst and molecular weight control agent in thereactor; however, it is preferable to melt blend or disperse thepolymerization catalyst and/or molecular weight control agent in amonomer melt or solid before charging them into the reactor. In the caseof the melt blending, temperature of the monomer melt is at least themelting point of polyester monomer, for example, preferably 85-200° C.,more preferably 90-120° C.

[0057] The amount of the monomer to be charged into the reactor may bemeasured on a weight or volume basis; however, it is preferable to carryout measurement on a volumetric capacity basis, using more inexpensive,simpler equipment. To be specific, valves are mounted on the upper andlower portions of a measuring vessel. With the lower valve closed up, amonomer melt is admitted into the vessel by opening the upper valveuntil the vessel is filled to capacity. Then, the monomer melt is fedinto the reactor by closing up the upper valve and opening the lowervalve. If a plurality of measuring vessels are interconnected, it iseasy to feed monomer melts to a plurality of reactors at the same time.The capacity of the measuring vessel may be on the same order as that ofthe reactor.

[0058] When a cyclic ester such as glycolide is subjected toring-opening polymerization, all the openings may be closed up to createa closed system. When poly-condensation by dehydration ordealcoholization is carried out using glycolic acid or its alkyl ester,water or alcohol, etc. should be evacuated from the opening.

[0059] The reactor with the monomers or monomer mixture charged thereinis heated from outside. No particular limitation is imposed on heatingmeans; however, when the reactor is small, it is preferable to use atemperature-controllable oil bath in which the reactor is immersed forheating to a predetermined temperature.

[0060] Alternatively, the reactor with the monomers or monomer mixturecharged therein may be heated with a jacket mounted on the outsidethereof, in which a heat transfer oil is circulated. Yet alternatively,that reactor may be placed in a circulating hot-air oven or heated fromoutside using an electrical heater. For industrial production purposes,the reactor may remain fixed in place. Alternatively, the reactor withthe monomers or monomer mixture charged therein may be transferred to anoil bath or a circulating hot-air oven, in which it may be held for agiven period of time.

[0061] In the present invention, a polyester is prepared by bulkpolymerization in the reactor. Then, the polyester is released from theinner surface of the reactor upon its volume shrinkage, whereby thepolyester can be recovered in a bulky mass from the reactor.

[0062] To shrink the volume of the polyester product, it is preferablycrystallized while it is in a molten or semi-molten state. In thepresent invention, it is preferred that the polyester such aspolyglycolic acid be crystallized in a later stage of polymerization orafter the completion of polymerization. The application of reactionconditions under which the polyester product is already crystallized atan initial stage of polymerization would not allow the polymerizationreaction to proceed satisfactorily, often causing large amounts ofunreacted materials (unreacted monomers) and low-molecular-weightmaterials (oligomer or low-molecular-weight polymer) to remain in thereactor. When the reaction temperature at the initial stage ofpolymerization is low, some heat may be applied at the later stage ofpolymerization so that the polyester product can be placed in a moltenor semi-molten (amorphous) state.

[0063] It is here noted that by the initial stage of polymerization isintended a stage where the amount of the remaining unreacted materialsis 50% or greater on a reaction start basis and by the later stage ofpolymerization a stage where the amount of the remaining unreactedmaterials is less than 50% on the same basis. To what degree thepolymerization reaction proceeds may be determined by the gas or liquidchromatography or NMR (nuclear magnetic resonance) of the unreactedmaterials.

[0064] At the later stage of polymerization or after the completion ofpolymerization, the polyester product may be crystallized by carryingout the reaction at a temperature lower than the melting point orcrystallization temperature of the polymer at the start time ofpolymerization or from the initial stage of polymerization; previouslyadding a crystal nucleating agent to the monomers; applying impacts onthe polyester product; cooling the polyester product; or the like. Inparticular, the crystallization by carrying out the reaction at atemperature lower than the melting point or crystallization temperatureof the polymer at the start time of polymerization or from the initialstage of polymerization, and the crystallization by cooling is preferredbecause it can be carried out in a stable, economical manner with nointroduction of impurities. It is here noted that the coolingtemperature should be lower than the melting point of the polyester.

[0065] As the volume of the polyester product such as poly-glycolic acidis shrunk by crystallization or the like, the release of the polyesterproduct from the releasable inner surface of the reactor becomes soready that the polyester product can be easily recovered in the form ofa bulky mass. The bulky mass is usually one single mass; however, it maybe broken down into some mass pieces although depending on thepolymerization conditions or post-treatment conditions used. It is hereunderstood that the recovery of the polyester product as a bulky massimplies that it can be taken out of the reactor with no need of crushingpolyester portions deposited onto the inner surface of the reactor, astirrer, etc.

[0066] No particular limitation is imposed on how to discharge theresulting polyester from the reactor in a bulky form. For instance, thismay be achieved by turning the reactor upside down; ejecting thepolyester from one of both end portion of the reactor; and sucking thepolyester from an upper opening in the reactor. Alternatively, a convexshape is imparted to a closing lid for the upper opening in the reactor,and a concave shape is forcibly imparted to the upper portion of a bulkyform of polyester product. Then, a member having a high coefficient offriction with the polyester product is inserted into the concaveportion, so that the polyester product is removed due to friction. Yetalternatively, a concave shape is imparted to the closing lid and aconvex shape is forcibly imparted to the upper portion of the bulkypolyester product, so that the convex portion of the product can begrabbed.

EXAMPLES

[0067] The present invention is now explained more specifically withreference to inventive and comparative examples.

Example 1

[0068] One hundred (100) grams of glycolide and 0.01 gram of tindichloride. 2H₂O were charged into a stainless steel (SUS304) metalcircular tube (reactor) of 24 mm in inner diameter and 350 mm in length,which tube was closed up at one opening with a silicone rubber stopper.Then, the other opening was closed up with a silicone rubber stopper.The said tube was immersed in an oil bath of 220° C. for ring-openingpolymerization by heating.

[0069] Three hours later, the said tube was taken out of the oil bath,and left standing for cooling over 2 hours. Two hours later, thesilicone rubber stoppers were put off and the said tube was placed in avertical state where it was lightly shaken so that a bulky mass ofpolyglycolic acid of 100 grams was discharged (with the recoveryyield=about 100%).

Example 2

[0070] One hundred (100) grams of glycolic acid were charged into astainless steel (SUS304) metal circular tube (reactor) of 24 mm in innerdiameter and 350 mm in length, which tube was closed up at one openingwith a silicone rubber stopper. Then, the said tube was immersed in anoil bath of 220° C. with the stopper down. Dehydration under a reducedpressure of 20 to 50 mmHg was carried our through the other opening inthe said tube. Two hours after the dehydration polycondensation wasperformed in this way, the distillation of condensed water was notfound. Then, the application of the reduced pressure and the heating ofthe oil bath were stopped, followed by spontaneous cooling.

[0071] Two hours later, the said tube was taken out of the oil bath thetemperature of which dropped to 100° C., and the silicone rubber stopperwas put off. Then, the said tube was lightly shaken in a vertical state,so that a bulky mass of polyglycolic acid of 76 grams was discharged(with the recovery yield=about 100%).

Example 3

[0072] One hundred (100) grams of glycolide and 0.01 gram of tindichloride. 2H₂O were charged into a stainless steel (SUS304), bottomedmetal circular tube (reactor) of 24 mm in inner diameter and 300 mm inlength, which tube had a taper gradient of 10%. Then, the said tube wasclosed up at an opening with a silicone rubber stopper. The said tubewas immersed in an oil bath of 220° C. for ring-opening polymerizationby heating.

[0073] Three hours later, the said tube was taken out of the oil bathand left standing for cooling over 2 hours. Two hours later, thesilicone rubber stopper was put off, and the said tube was turned upsidedown, instantaneously whereupon a bulky mass of polyglycolic acid of 100grams was discharged due to its own weight (with the recoveryyield=about 100%).

Example4

[0074] One hundred (100) grams of glycolide and 0.01 gram of tindichloride. 2H₂O were charged into a stainless steel (SUS304) metalcircular tube (reactor) of 24 mm in inner diameter and 350 mm in length,which tube was closed up at one opening with a silicone rubber stopperand had been coated on its inner surface with a releasing agent(“Die-Freew” made by Daikin Kogyo Co., Ltd.). Then, the other opening,also, was closed up with a silicone rubber stopper. The said tube wasimmersed in an oil bath of 220° C. for ring-opening polymerization byheating.

[0075] Three hours later, the said tube was taken out of the oil bath,and left standing for cooling over 2 hours. Two hours later, thesilicone rubber stoppers were put off and the said tube was placed in avertical state, instantaneously whereupon a bulky mass of polyglycolicacid of 100 grams was discharged (with the recovery yield=about 100%).

Example5

[0076] Two thousands (2,000) grams of glycolide and 0.06 gram of tindichloride. 2H₂O were melt-blended and then charged into a jacketed,stainless steel (SUS304) rectangular reactor (the dimensions of theupper opening: 300 mm in length and 30 mm in width dimension and thedimensions of the closed lower portion: 294 mm in length, 26 mm in widthdimension and 200 mm in depth). Then, the opening was closed up with astainless steel (SUS304) plate. While the inner surface of the reactorwas not buffed, the reactor had a tapered structure extending linearlyform the top of the opening to the bottom of the closed portion. Thejacket structure was applied to the whole surface of the reactor exceptthe upper opening. The ring-opening polymerization was carried out byforcibly circulating a heat transfer oil of 170° C. through the jacket.Seven (7) hours later, the heat transfer oil circulated through thejacket was cooled, thereby cooling the whole rectangular reactor. Then,the upper steel plate was put off and the rectangular reactor was turnedupside down through 180°, instantaneously whereupon a bulky polyglycolicacid product of 2,000 grams was discharged (the recovery yield=about100%).

Example 6

[0077] Four hundreds (400) grams of glycolide and 0.012 gram of tindichloride. 2H₂O were melt-blended and then charged into a jacketed,stainless steel (SUS304) circular tube (reactor: 28 mm in insidediameter and 500 mm in length with the top opening and the bottomclosed). Then, the upper opening was closed up with a stainless steel(SUS304) plate. While the said tube had no tapered structure, its innersurface was buffed (with buff No. 300). The jacket structure was appliedto the whole surface of the reactor except the upper opening. Thering-opening polymerization was carried out by forcibly circulating aheat transfer oil of 170° C. through the jacket. Seven (7) hours later,the heat transfer oil circulated through the jacket was cooled, therebycooling the whole said tube. Then, the upper steel plate was put off andthe said tube was turned upside down through 180°, instantaneouslywhereupon a bulky mass of polyglycolic acid of 400 grams was discharged(the recovery yield=about 100%).

Example7

[0078] Example 1 was repeated with the exception that 90 grams ofglycolide, 10 grams of L-lactide and 0.01 gram of tin dichloride. 2H₂Owere used for a 5-hour polymerization. As a result, a bulky form ofglycolide-lactide copolymer of 100 grams was discharged from the metalcircular tube (the recovery yield=about 100%).

Example8

[0079] Example 1 was repeated with the exception that 80 grams ofglycolide, 20 grams of L-lactide and 0.01 gram of tin dichloride. 2H₂Owere used for a 5-hour polymerization. As a result, a bulky form ofglycolide-lactide copolymer of 100 grams was discharged from the metalcircular tube (the recovery yield=about 100%).

Example9

[0080] Example 1 was repeated with the exception that 95 grams ofglycolide, 5 grams of L-lactide and 0.003 gram of tin dichloride. 2H₂Owere used for a 24-hour polymerization at 170° C. After the completionof polymerization, the metal tube was removed out of the oil bath,immediately after which the silicone rubber stopper was put off with nocooling. As a result, a bulky form of glycolide-lactide copolymer of 100grams was discharged from the metal circular tube (with the recoveryyield=about 100%).

Example10

[0081] Example 1 was repeated with the exception that 95 grams ofglycolide, 5 grams of trimethylene carbonate and 0.003 gram of tindichloride. 2H₂O were used for a 7-hour polymerization at 170° C. Afterthe completion of polymerization, the metal tube was removed out of theoil bath, immediately after which the silicone rubber stopper was putoff with no cooling. As a result, a bulky form of glycolide-trimethylenecarbonate copolymer of 100 grams was discharged from the metal circulartube (with the recovery yield=about 100%).

Comparative Example 1

[0082] One hundred (100) grams of glycolide and 0.01 gram of tindichloride. 2H₂O were charged into a bottomed glass test tube of 24 mmin inner diameter and 350 mm in length. Then, the test tube was closedup at an opening with a silicone rubber stopper. This test tube wasimmersed in an oil bath of 220° C. for ring-opening polymerization byheating.

[0083] Three hours later, the test tube was taken out of the oil bathand left standing for cooling over 2 hours. In the cooling process, theglass cracked noticeably, indicating that a part of the test tube wasbroken. Two hours later, the polyglycolic acid product was taken out ofthe test tube. It was found that glass fragments were stuck to thesurface of a bulky mass of polyglycolic acid. The glass fragments stuckto the polyglycolic acid were ground off by a grinder. Consequently, theamount of the polyglycolic acid recovered was barely 85 grams (therecovery yield was about 85% by weight).

Comparative Example 2

[0084] One hundred (100) grams of glycolide and 0.01 gram of tindichloride. 2H₂O were charged into a stainless steel (SUS304) reactorequipped with a stirrer, wherein they were heated to 220° C. underagitation for ring-opening polymerization.

[0085] One hour later, the viscosity of the reaction system becamerapidly too high for stirring. After cooling, the polyglycolic acidproduct fixed to the stirrer was recovered by means of a cold chisel, achisel, a fretsaw or the like. As long as ten hours were needed forrecovery with increased losses; the amount of the poly-glycolic acidrecovered was barely 92 grams (the recovery yield was about 92%).

INDUSTRIAL APPLICABILITY

[0086] According to the present invention, there is provided a polyesterproduction process by bulk polymerization in a reactor apparatus, whichenables the resulting polyester to be readily recovered in the form of abulky mass after the completion of polymerization reactions.

[0087] According to the present invention, it is thus possible toreadily recover the resulting polyester from the reactor after bulkpolymerization by making use of the volume shrinkage of the polyesterand the releasability of the polyester from the inner surface of thereactor.

[0088] According to the present invention, there is also provided areactor apparatus for bulk polymerization for polyesters, which is bestsuited for such a polyester production process.

1. A polyester production process by bulk polymerization in a reactorapparatus, characterized in that the volume of the resulting polyesteris shrunk to release the same from the inner surface of the reactor, sothat the polyester can be recovered in the form of a bulky mass from thereactor.
 2. The production process according to claim 1, wherein theresulting polyester is crystallized to shrink its volume.
 3. Theproduction process according to claim 1, wherein the inner surface ofthe reactor is free from asperities that come into contact with theresulting polyester and disturb its discharge.
 4. The production processaccording to claim 1, wherein there is no stirrer in the reactor.
 5. Theproduction process according to claim 1, wherein the reactor has atleast its inner surface formed of a metal.
 6. The production processaccording to claim 1, wherein the inner surface of the reactor has beentreated with a releasing agent.
 7. The production process according toclaim 1, wherein the reactor is a tubular member.
 8. The productionprocess according to claim 7, wherein the reactor is a tubular memberopen at both ends, and at least one of the openings is closed up duringa polymerization reaction.
 9. The production process according to claim7, wherein the reactor is a tubular member having a bottom and anopening.
 10. The production process according to claim 7, wherein thetubular member has a tapered structure.
 11. The production processaccording to claim 10, wherein the tapered structure has a gradient of 1to 50%.
 12. The production process according to claim 1, wherein thepolyester is an aliphatic polyester.
 13. The production processaccording to claim 12, wherein the aliphatic polyester is apolyhydroxycarboxylic acid.
 14. The production process according toclaim 13, wherein the polyhydroxycarboxylic acid is polyglycolic acid.15. The production process according to claim 14, wherein thepolyglycolic acid is a polymer obtained by the ring-opening ofglycolide.
 16. A reactor apparatus for bulk polymerization forpolyesters, which is capable of being heated from outside and formed ofa material having heat resistance enough to stand up to a bulkpolymerization temperature for polyesters, and has an inner surfacecapable of releasing the resulting polyester upon its volume shrinkage.17. The reactor according to claim 16, wherein the inner surface is freefrom asperities that come into contact with the resulting polyester anddisturb its discharge.
 18. The reactor according to claim 16, whereinthere is no stirrer inside.
 19. The reactor according to claim 16, whichhas at least its inner surface formed of a metal.
 20. The reactoraccording to claim 16, which is a tubular member.
 21. The reactoraccording to claim 20, which is a tubular member open at both ends,wherein at least one of the openings is closed up during apolymerization reaction.
 22. The reactor according to claim 20, which isa tubular member having a bottom and an opening.
 23. The reactoraccording to claim 20, which is a tubular member having a taperedstructure.
 24. The reactor according to claim 23, wherein the taperedstructure has a gradient of 1 to 50%.